Not Applicable.
This invention relates generally to threaded fasteners such as nuts and bolts and more particularly to threaded fasteners having an improved thread and reduced tolerances and improved fastening.
Threaded fasteners are well known to the art. One goal of threaded fasteners, particularly nut and bolt combinations or threaded pipes, is to provide a fastener that stays tightened and does not loosen in use. Generally accepted matching techniques result in tolerances between the nut an bolt threads and there is clearance or play which allows for movement between the elements. For example, a fastener or nut and bolt can loosen under load or vibration.
Another goal of threaded fasteners is to form seals. Currently, in order to obtain a tight joint or seal for holding gasses and liquids in an application where a lute or sealer would cause contamination or where liquid or gas would attack and destroy the seal, a Dryseal form of pipe thread is used.
Fixed, threaded installations, such as plugs, oil and grease fittings use straight Dryseal (NPSF) for internal and tapered Dryseal (NPTF) for external threads. The hole is tapped straight to facilitate production, especially for multiple tapping, as it is not necessary to stop tapping at a given depth to ensure size.
What occurs, is that there is a fixed position that will be reached as soon as the tapered thread meets the opposing flank. Therefore, there is no possible adjustment axially.
When vibration is a factor in the connection of, for example, two pipes, the Dryseal applies with tapered internal and external threads.
There are several prior art systems that try to remedy the problem of clearance which results in loose connections due to vibration. Locknuts are used with a nylon washer locked in at the end of the nut. When the nylon washer contacts the bolt, it tightens around the thread and locks the nut in position. Locknuts have disadvantages. The nylon portion of nut has no load carrying threads. Further, it requires more material to make the nut longer and the nylon washer and the nut must be made separately and then crimped together. The locknut of this type can be used only a few times, is not as resistant to heat and requires chemicals i.e. nylon.
Deformed nuts have been used to overcome the loosening problem. These comprise nuts that are deformed out of the circular shape and made into rounded-off triangle shape. Then the bolt engages the threads, it contacts three points and the nut locks around the bolt. However, only heat-treated nuts can be used. To make the deliberate deformation requires an expensive manufacturing set-up. Further, the process is very slow. Also, the reaction of each individual nut is variable, which makes it difficult to predict or guarantee tolerances. Moreover, it can only be used with nuts.
A spiral lock is a lock thread is a commercially available alternative. However, the spiral lock provides an interference on the outside diameter of the bolt. It is difficult to control the interference with accuracy. The surface of the bolt thread can cause galling of the nut and subsequent failure.
Interference-fit threads are used which include a complete interference of the matching parts at the flanks to provide an interference or metal flow. However, based upon accepted machining practices, it is very difficult to produce, for example, class 5 threads (Federal Standard Screw-Thread Standards For Federal Services-Class 5 Interference Fit Screw Threads).
Examples of prior art fastener technologies are disclosed in the following U.S. Pat. No. 1,369,156, to Woodward; U.S. Pat. No. 2,842,180, to Brown et al; U.S. Pat. No. 3,459,250 to Tabor; U.S. Pat. No. 3,661,194, MacFarlane et al.; U.S. Pat. No. 3,721,283, to Evans; U.S. Pat. No. 3,850,215, to Orlomoski; U.S. Pat. No. 3,927,503, to Wilson; U.S. Pat. No. 4,023,914, Holmes; U.S. Pat. No. 4,071,067, to Goldby; U.S. Pat. No. 4,396,321, Holmes; U.S. Pat. No. 4,846,614, to Steinbock; and U.S. Pat. No. 5,194,214, to Snyder et al.
However, these prior examples may not form good seals. In my prior patent, U.S. Pat. No. 5,944,465, which is incorporated herein by reference, I disclosed a low tolerance threaded fastener which overcomes many of the above noted problems. The fastener disclosed in the U.S. Pat. No. 5,944,465 patent works well for its intended purpose. However, it can be improved upon, specifically to form a dry seal between two threaded elements.
A threaded member such as a bolt, nut, or pipe has a threaded portion on a body of the member. The threaded portion of the member includes a first threaded section, a second threaded section, and a third threaded section. The first and third threaded section have standard threads which comprise standard roots, flanks, and crests. The second section is between the first and third sections and has threads in which a portion of the threads are raised relative to the standard threads to define bumps. The raised sections or bumps comprise a raised root, a raised flank, and a raised crest. The raised root and raised crest define diameters different from the diameters of the standard root and standard crest, respectively. In an exteriorly threaded member, the raised root and crest have diameters greater than the diameter of the standard root and crest, respectively. In interiorly threaded member, the raised root and crest define diameters smaller than the diameters of the standard root and crest, respectively.
The raised bump or section on the threaded member forms a low tolerance threaded fastener which can be used to form dry seals.